can you narrow down what extrusion you are trying to access... there are several, like
Extrude features to 3D symbology—ArcGIS Pro | ArcGIS Desktop
maybe a screen grab would help
Is the layer that you wish to extrude in the 2D Layers or 3D Layers group?
If 2D, drag it into the 3D group and try extruding.
I figured it out…I’m really new to this and I didn't realize I wasn't in Scene.
I have a filled polygon that I would like to lay flat on the earth (which isn't flat) under my extruded layer so parts are not showing under my extruded layer in Scene.
From the documentation that Dan sent (Extrude features to 3D symbology—ArcGIS Pro | ArcGIS Desktop ) which extrusion type are you using? Do you have a screenshot of what you see in addition to an explanation of what is wrong about that and what you would like to see?
THanks for your help. I'm learning a lot. I figured it all out and realized that the layer needs to be in 2D not 3D in order for it to drape on the terrain! Sometimes the obvious things aren't apparent right away.